Internal combustion engines are widely used and their operation is well known. Typically, air for fuel combustion is provided to each firing chamber via individual runners from a central intake air manifold. Acceleration and speed in a naturally aspirated, spark ignition engine are controlled typically by a rotary throttle valve that may be controlled by an operator to variably restrict the volume of air allowed to enter the manifold at any time.
Under engine idle conditions, the throttle valve blade very nearly closes of the throat of the throttle plate assembly, creating a substantial sub-atmospheric vacuum within the manifold. When the throttle valve is opened, the vacuum causes an immediate inrush of air into the manifold. This flow spike is solely in response to the manifold vacuum and the initial filling of the manifold vacuum with air and precedes the actual increase in airflow demand of the engine that occurs as engine speed increases.
The rapid filling of the manifold plenum results in turbulent air flow at the leading and trailing edges of the throttle valve blade and downstream of the valve cross-shaft when the air flows around the shaft are recombined. Such turbulent air flow is characteristic of all throttled engines, to varying degrees, and causes a rushing noise known in the art as “tip-in” noise. This noise is most noticeable when the throttle is quickly opened by rotating the blade through about the first 30° of opening rotation.
It is known to try to reduce tip-in noise by extending a coarse screen across a portion of the throttle throat below the throttle valve. Drawbacks of this approach are a) an increased number of parts, and therefore increased cost of engine manufacture; and b) a fixed flow restriction of incoming air at all flow conditions, some of which would enjoy a non-screen-restricted air flow.
What is needed is a means for minimizing tip-in noise during opening of an engine throttle valve, without creating a permanent air flow restriction.
It is a principal object of the present invention to minimize tip-in noise of a naturally aspirated internal combustion engine while permitting unrestricted air inflow as required by engine speed and acceleration.